My family is from Rio Grande and I grew up with El Yunque as my panoramic view.
Yes it always has been activities in the Yunque and they own land also. My brother and a friend back in the 70s got caught for getting to close to it,
they witness what looked like scientist coming in and out of the places and they also saw cages in the back of trucks.
Because they were only minors they were just taking home and not charges were filed.
You can go around the area where the government facility is located but you need permit to enter.
Occurs the area is not advertised and only have government property signs and we were told that is just a weather station.
It has been in EL Yunque as long as I can remember.

